Field of the Invention
Aspects of the present invention relate generally to wireless communications network technologies, and more particularly, to processes for managing the hybrid automatic repeat request (HARQ) process when the uplink and downlink configuration is changed in a Time-Division Duplex (TDD) system.
Description of the Related Art
In the 3GPP (Third-Generation Partnership) LTE (Long Term Evolution) system, a HARQ mechanism is used to improve the reliability of uplink and downlink data transmission. A DL HARQ is an asynchronous adaptive HARQ, and a UL HARQ is a synchronous adaptive or non-adaptive HARQ. The adaptive HARQ is a modulation and code scheme (MCS) of the retransmission data and allocated physical resources can be changed with the channel state information (CSI). Synchronous HARQ means that the interval between the first transmission and a retransmission is a fixed time. Compared with the traditional stop-and-wait ARQ mechanism, the LTE system can support multiple parallel HARQ processes. For the asynchronous DL HARQ, the ID of a user equipment (UE) DL HARQ process should be informed in downlink control information (DCI). The UE can correctly combine the retransmission data with the first transmission data. The interval between the first transmission and the retransmission of the DL HARQ is not fixed, but the interval between the DL HARQ-ACK and the corresponding physical downlink shared channel (PDSCH) should follow a fixed interval. For the synchronized UL HARQ, it is unnecessary to indicate the ID of the UL HARQ process. The interval between the first transmission and the retransmission of the UL HARQ is fixed. Besides, the interval between the UL HARQ-ACK and the corresponding physical uplink shared channel (PUSCH) should follow a fixed interval. An uplink scheduling signaling comprises a UL grant and a physical HARQ indicator channel (PHICH), wherein the UL grant can be used to schedule new data transmission and adaptive/non-adaptive HARQ retransmission, and the PHICH only can be used to schedule the non-adaptive HARQ retransmission. In the FDD LTE system, the uplink and downlink only can support eight parallel HARQ processes, and there is only a HARQ-ACK/uplink scheduling timing. The HARQ-ACK is fed back after 4 ms after the data is received, and the uplink scheduling signaling is transmitted prior to 4 ms before the uplink data is transmitted. In the TD-LTE system, a maximum number of HARQ processes is related to the UL-DL configuration. When the ratio of the UL subframe in a radio frame is increased, the number of UL HARQ process will be increased, and the number of DL HARQ processes will be reduced. There are corresponding HARQ-ACK feedback timing and uplink scheduling timing for each UL-DL configuration.
However, following the existing HARQ-ACK feedback timing and uplink scheduling timing will have some problems when the UL-DL configuration is changed.